I took in a spayed female breeder relaese dog about 6 years ago. She is a wonderful dog happy go lucky. Loves to eat shop and play. The only problem I have is if we are at Petsmart and another dog comes up to smell her(no matter size breed gender) she will snarl and nip or bite at the other dog. She has no problems walking by being near...just when they look at her or sniff her. What can I do to stop this?